1. Field of the Invention
The present invention relates to a security monitoring system which detects, for example, the occurrence of an intruder or a fire in a home or a building, indicates the occurrence of an emergency situation, or the like to accomplish crime prevention, diasaster prevention, emergency rescue handling, etc. by quickly taking necessary measures.
2. Description of the Prior Art
A security monitoring system includes a plurality of terminal units, installed, for example, at an entrance, window, etc. through which an intruder may enter, or installed at various spots where a fire may break out, in order to detect a suspicious intruder or an occurrence of a fire in a home, a building, or the like, and a processing apparatus which receives en bloc signals that are detected at these terminal units to display an alarm or take other necessary measures. The processing apparatus, too, is generally installed at a prescribed spot in a home, a building, or the like where the terminal units are installed for detection. When a terminal unit for detection detects an intruder, occurrence of a fire, or the like, the processing apparatus notifies the occupants, employees, or the superintendent of the home or the building, as well as informs the monitoring center of the security company, for example, via the telephone circuit as the need arises. The terminal unit is not only a terminal unit for detection which is installed at a prescribed place and is used for detecting an intruder, occurrence of a fire, or the like, as described above, but also, the terminal unit may be used for signaling a device which is carried by the operator such as the occupant or the superintendent of the home or the building for informing of the occurrence of an emergency situation, such as a sick or injured person, or for providing an indication at the home or the building where the system is installed that the occupant or the superintendent is at or away from the home or building.
Such a terminal unit for detection or terminal unit for notification (signaling) is linked, to simplify the wiring work for example, to the processing apparatus by radio through the use of a radio transmitter, and is constructed as a radio transmitter for detection or a radio transmitter for notification. Generally, for a radio transmitter there is a coverage area which is determined corresponding to the intensity of the transmitted radio waves, so that the processing apparatus that receives the radio waves transmitted from the radio transmitter has to be installed within the coverage area of the transmitter.
Therefore, in installing each of the radio transmitters and the processing apparatus for a security monitoring system, they are to be installed to have their mutual separation within the coverage area of the radio transmitter, and in addition, a test is arranged to be made as to whether the processing apparatus can receive the signals reliably under the installation conditions.
However, even when each of the radio transmitters and the processing apparatus are installed properly and the transmission and reception tests between them were given properly, the intensity of the transmitted radio waves from the radio transmitter is sometimes reduced, because of the variations in the characteristics of the radio transmitter under the various influences such as temperature in the surroundings, variations in the power supply voltage, and scattering in the characteristics of each of the constituent parts. Consequently, even when the radio transmitter and the processing apparatus are installed to be within the coverage area in the normal conditions, and it is confirmed at the time of installation through the transmission and reception tests that they were definitely operating, the transmitted power of the radio transmitter is reduced and fails sometimes to reach the processing apparatus under the least favorable conditions, since the tests at installation are not carried out by considering the state in which the transmitted intensity is reduced, in particular, to the worst condition. Because of this, there exists a problem that even with a security monitoring system which operated normally at the time of installation, the transmitted power from the radio transmitter fails to reach the processing apparatus if, in its state of use, it finds itself in the worst condition due to a drop in the voltage of the power supply or a change in the surrounding temperature, and is unable to detect an intruder or occurrence of a fire, for instance, without failure. Accordingly, it has not been possible to ensure the shortest life for the security monitoring system.